1. Field of the Invention
The present invention relates to a projection display apparatus for displaying a projected image on a screen and an actuation control method thereof.
2. Description of the Related Art
In recent years, liquid crystal projectors have become quite popular as a projection display apparatus for displaying a projected image. The liquid crystal projector is configured to modulate light emitted from a light source by using a liquid crystal panel and form an optical image in accordance with image signals, and then display the optical image that is enlarged by a projection lens on a screen.
For a liquid crystal projector having such a configuration, it has been proposed that a projection lens is vertically and horizontally shifted in a plane normal to the projected optical axis, to thereby enable adjustment of the position of an image display on a screen. However, when shifting the projection lens for a long distance (i.e., the motion quantity is large), part of the projection lens may undesirably go outside of a display panel of a liquid crystal panel which is a light modulating element, resulting in the occurrence of a so-called “picture defect,” loss of a projected image on a screen. To avoid this, when shifting a projection lens, it is desirable to prevent the occurrence of picture defects by limiting two-dimensional shift quantity in the vertical and horizontal directions.
In the case where a projection lens is two-dimensionally shifted as shown in, for example, FIG. 13, a movable range of the projection lens describes a rectangular shape, whereas a range in which no picture defects occur describes a circular or elliptical shape. Therefore, it is desirable that the two-dimensional shift quantity of the projection lens may be limited such that the center of the projection lens does not go outside of the circular or elliptical range, in which no picture defects occur (see, for example, Japanese Unexamined Patent Application Publication No. 2005-173460).